Fuel control system for turbojet engines



Sept. 4, 1951 E. M. REDDING 2,565,373

FUEL CONTROL SYSTEM FOR TURBOJET ENGINES Filed Jan. 10, 1946 2Sheets-Sheet 1 Inventor Attorney Edward M. Redd/fig Sept. 4, 1951 E. M.REDDING FUEL CONTROL. SYSTEM FOR TURBOJET ENGINES Filed Jan. 10, 1946 2Sheets-Sheet 2 Edward M. Re dd/ng Patented Sept. 4, 1951 FUEL CONTROLSYSTEM FOR TURBOJET ENGINES Edward MtRedding, United States hlavyApplication January 10, 1946, Serial No. 640,293

1 Claims. (cl. so-ass) (Granted under the act of March 3, 1883,15

This invention relates to aircraft propulsion motors of the reactiontype and in particular to their fuel systems.

An object of the invention is to deliver auxiliary fuel to a reactionmotor so that a desired optimum exhaust temperature may be maintainedirrespective of variations in flight conditions. Another object is toutilize a single fuel governor control to supply fuel to both themainand auxiliary fuel systems of a reaction motor "so that therespective rates of flow of the latter two will be under control of theformer. I

Further objects, advantages and salient feat tures of the inventionswill become apparent from the following description, accompanying drawings and appended claims.

. In the drawings; Fig. 1 represents one embodiment of the invention andshows a longitudinal section of a generally conventional reaction motortogether with a diagrammatic illustration of a a fuel sys- Fig. 2;

Fig. 4 is a similar modification, wherein the orifice is madeadjustable; and

amended April 30, 1928; 3'70 0. G. 757') The auxiliary systemisessentially a reheat de vice which raises the temperature of gasespreviously cooled by expansion. It may function in the manner previouslydescribed, that is, to' increase the thrust of the unit or may reheatthe gasesfor subsequent use in another gas turbine stage as shown e. g.in Fig. 5. It is contemplated. accordingly, that another gas turbine 5'could be used in the gas flow-downstream from the auxiliary fuel supply.It is apparent, also, and contemplated, that more than one auxiliaryfuel system could be used where successive gas reheat 1 would beadvantageous as e. g., fuel manifolds 9 and 9' with flame holders H andII, ignition 's'ystemsproposed or used prior to this invention have notgivenoptimum performance under variable flight conditions because oflack of proper control of the auxiliary fuel. It is apparent that if theauxiliary system supplies less than an optimum amount of fuel, the gastemperature in the exhaust pipe will beless than the materials arecapable of withstanding and hence the highest performance of the unitwill not be obtained,

Fig. 5 illustrates a modification, wherein the arrangement shown in Fig.1 is "supplemented by additional turbine and reheat devices.

Referring to Fig. 1, I represents a reaction motor having a compressor2, main fuel supply manifold 3, combustion chamber 4, gas turbine 5 andtail cone 6. Fuel delivered by the manifold is burned in the combustionchamber by air delivered from the compressor, the products of combustionpassing through and drivin the turbine, which in turn drives thecompressor. The products of combustion then pass into exhaust pipe I andissue from nozzle 8 providing thrust for the unit. These features areregarded as conventional in the art.

In the exhaust pipe I a manifold 9 is provided which delivers fuel intothe gas flow by means of a plurality of jets, its combustion raising thetemperature of the exhaust gases, adding to their kinetic energy whichincreases the thrust of the unit over that which would be obtained bythe main fuel system alone. At III is illustrated a suitable ignitiondevice to initiate combustion of the fuel supplied by manifold 9 and IIis a flame holder to maintain uniform combustion. These latter twodevices are conventional in the art.

whereas, if more than an optimum amount of fuel is introduced thetemperatureswill be higher than the materials are capable ofwithstanding and their useful life will be materially impaired. Anoptimum fuel flow would be one such that the temperatures are themaximum which the materials can withstand for a certain desired usefullife'or that which effects an improved overall thermal cycle.

It has been found that at constant R. P. M. the exhaust pipetemperature, resulting from the addition of auxiliary fuel, can be keptsubstantially constant under variable flight conditions if the amount offuel introduced into the auxiliary system bears a fixed relationship orratio at all times to the main fuel supply. The system herein describedaccomplishes this desirable result.

At 12 is diagrammatically illustrated a governor which at any particularthrottle setting will control the delivery of fuel to a combustionchamber at such a rate that constant turbine speed will be branch tometering device I]. These two devices are constructed in much the samemanner as conventional gear pumps and together they constitute aproportional fuel divider 30. They are connected by a shaft I8 50 thatthey operate in unison, but are not mechanically driven, the rotation ofthe gears being effected by the flow of fuel through the devices. Theyare so proportioned in size that their respective delivery rates are ina fixed ratio regardless of total rate of flow. Alternately, they couldbe made the same size and be suitably connected by gearing such thattheir respective rates of fiow would be in proportion to their rates ofrotation.

Meterin device l6, which would normally be designed to deliver a smallerquantity of fuel than H, due to the normally smaller requirements of theprimary combustion chamber. is connected to the main fuel manifold 3 byline iii. The other metering device I1 is connected to the auxiliaryfuel manifold 9 by line 20. A valve 2| is provided in line 20 to renderthe auxiliary supply inoperative when its useis not desired. A line 22by-passes the metering device It and is provided with a valve 23 whichis connected to valve 2| by link 24 so that the two valves operate inunison, and when valve 2| is closed, valve 23 is open. Valves 2| and 23are not metering valves, but simple cut-off valves linked together forreverse operation. This link may, if desired, be connected to the pilotsthrottle so that valves 2| and 23 are under control of the throttle onlyas it is moved to its full throttle position; that is, under normalpower requirements only the main fuel system leading to manifold 3 wouldbe in use but when full power is desired movement of the throttle tofull open position would render the auxiliary system leading to manifold9 operative also. Throttling is at all times controlled by adjustment ofthe governor I2. When 2| is closed and 23 opened, metering device beingof the positive displacement type will not operate. This in turn willpreclude shaft l8 from rotating and render metering device I6inoperative, the entire flow then passing through by-pass line 22.

While the metering devices above described are of the gear type, it isapparent from the teachings of the invention that other functionalequivalents will suggest themselves, and could be employed, to achievethe same ultimate results. It is contemplated that all metering deviceswhich will distribute liquid to a plurality of discharge lines in amanner to efiect a constant ratio of mass flow between the respectivedischarge lines, are within the spirit and scope of the invention.

Fig. 2 illustrates another embodiment of a fuel system which willachieve substantially the same results as the one previously described.Primed figures represent parts corresponding to those of Fig. 1. In thisembodiment the discharge line from governor l2 branches at l in the same-manner as the other embodiment, a portion of the fuel being deliveredto the main fuel system 3 by line l9 and the remaining portion toauxiliary manifold 9 by line 20. This line is provided with a valve 2|to render the auxiliary supply inoperative, when its use is not desired,and an orifice 25 which will meter a constant pro- 4 portion of thedischarge of governor l2 to th auxiliary system. The ratio of flowsthrough I l and 20' may be adjusted for optimum exhaust temperaturebythe choice ofa suitable orifice. The fixed orifice 25 may comprise anorifice as shown at 25" in Fig. 4. which is adjustable by means ofneedle'valve 21; this orifice would be so designed that its area couldbe adjusted by manual operation of the needle 21 during staticcalibration tests of the engine to maintain the proper fuel flow ratioto the main and auxiliary fuel injectors. The area so found is heldconstant during operation of the engine, or until further calibrationtests are made at a later date.

In lieu of a fixed orifice as previously described, the orifice could bemade adjustable by usin an adjustable valve 25' as shown in Fig. 3 inplace of the fixed orifice 25 shown in Fig. 2,

or the fixed orifice 25" shown in Fig. 4. Thisvalve 25' could be placedunder manual control of the pilot, who would make the adjustments inaccordance with observed indications of the temperature at the exhaustpipe to produce and maintain a fuel fiow such that a desired exhaustpipe temperature would be maintained. The-use of the adjustable valve 25under control of the pilot is for the purpose of placing the ratio offuel fiows to the two combustion stages wthin the control of the pilotduring flight. The advantage of this device lies in being able toprecisely regulate the temperature of the gases from the auxiliarycombustion chamber to a fixed valve. When the area of the orifice ismaintained constant during a flight through various altitudes at a R. P.M. of the engine, calculations show that the exhaust gas temperaturewould var slightly. Adjustable valve 25 would allow the pilot torectifythis, getting an indication of the exhaust gas temperature onhisinstrument board from a thermo-' couple or a similar device in theengine exhaust pipe, neither the thermocouple or other device being hereil lustrated, as not a part of the invention.

As an added refinement, however, to obtain more precise temperaturecontrol the valve could be automatically controlled by a barometricdevice 26, as shown in Fig. 3, which would function to regulate theauxiliary flow in response to I changes of air pressure which is relatedto the resultin changes in the exhaust pipe temperatures due to changesin altitude at constant turbine speed.

The governor I2 maintaining constant turbine R. P. M. has nothing to dowith orifice 25, valve 25, and barometric device 26. The governoroperates independently of the proposed metering device and any of itsparts.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What I claim is:

l. A reaction motor having a, first stage combustion chamber providingases for driving a turbine, and one or more additional stage combustionchambers for additional power generation, a fuel injector for each ofsaid chambers, a governor controlled fuel metering means for supplyingfuel under pressure at a controlled rate, a distribution system betweensaid metering means and said injectors, including a proportional fueldivider means operated in response to said fuel pressure, a supplyconduit from said metering means to said divided means, a fuel deliveryline for delivering one portion of the fuel from said divider means tothe first stage fuel injector, a second fuel delivery line fordelivering the remainder of the fuel from said divider means to theremaining fuel injectors, a by-pass conduit from said supply conduit tosaid first delivery line, cut-off means in said by-pass conduit and insaid second fuel delivery line, and control means for operating saidcut-off means simultaneously so that when one is open the other isclosed, whereby all the fuel may be selectively delivered eitherdirectly through said by-pass conduit into said first stage injector orproportionally through said divider means and said delivery lines intosaid first and additional stage injectors, irrespective of the rate ofthe total fuel supply.

2. A reaction motor as defined in claim 1 wherein said proportional fueldivider means comprises a pair of positive displacement gear pumpshaving a common drive shaft and a common inlet connected to said supplyconduit, the outlet of one of said gear pumps being connected to saidfirst fuel delivery line and the outlet of said other gear pump beingconnected to said second fuel delivery line, whereby when the cutoffmeans in said by-pass conduit is closed the fuel supply will bedelivered proportionally to the first and second delivery line inaccordance with the relative capacities of said gear pumps, and when thecut-off means in said by-pass conduit is open, the fuel divider will notoperate, but all the fuel will be delivered to said first delivery line.

3. A reaction motor as defined in claim 2 wherein the gear pumpconnected to said first fuel delivery line has a smaller capacity thansaid other gear pump, in accordance with the relatively smaller fuelrequirements of the primary combustion chamber, when the fuel is beingdelivered through said fuel divider.

4. A reaction motor as defined in claim 1 wherein said proportional fueldivider means comprises an open passage to said first fuel deliveryline, and a restricted passage to said second delivery lineprecalibrated to deliver the desired proportions of the fuel suppliedthrough said delivery lines.

5. A reaction motor as defined in claim 4 wherein said restrictedpassage comprises a fixed restriction.

6. A reaction motor as defined in claim 4 wherein said restrictedpassage comprises an adjustable restriction, with means for presettingthe adjustment during calibration under static tests.

7. A reaction motor as defined in claim 4 wherein said restrictedpassage comprises a metering valve for manual control during motoroperation.

EDWARD M. BEDDING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,238,905 Lysholm Apr. 22, 19412,409,176 Allen -Oct. 15, 1946

